For the file not found it's probably because you're using a separate /boot partition? If that's the case copy message.elyssa somewhere in /boot and edit /boot/grub/menu.lst to reflect that (make sure to remove /boot from the path.. since on that partition /boot here means / over there..).

You can simply right click on mintMenu and change the name of the menu in the preferences. The reason why it's still Cassandra is because it's saved in gconf within your personal data (which ultimately resides somewhere in /home ). So you're running Elyssa but your data is telling mintMenu that its name is Cassandra